1. Field of the Invention
The present invention relates to an electric discharge machine having a function to automatically calculate a weight of a workpiece.
2. Description of the Related Art
In electric discharge machining, an electrode gap formed between a workpiece and an electrode is exposed to high temperature and a moisture amount in machining liquid is reduced, or a moisture amount in machining liquid is reduced by natural evaporation in some cases. If the moisture amount is reduced in machining liquid in which water and oil are mixed, this could be a cause to largely reduce machining speed of the electric discharge machining or to hinder stable electric discharge machining.
To solve this problem, JP 2012-192512 A discloses an electric discharge machine including a measuring device for measuring a weight of machining liquid using a measuring tank, a water supply device for supplying water to the machining liquid, computing means for computing a reduction amount of water in the machining liquid based on the weight of the machining liquid measured by the measuring device, and a controller having control signal generating means for generating a control signal which operates the water supply device based on the reduction amount computed by the computing means.
When a weight of a workpiece is measured in a wire electric discharge machine, it is general to measure the weight using a scale, but when a workpiece having a large weight is to be measured, it is necessary to prepare a large measuring device, and there is a problem that the measuring operation requires labor.
When a workpiece to be electric discharge machined is placed on a table in a machining tank, there is a problem that a machine body of a casting or a guide is distorted under the influence of the weight of the workpiece, and a pitch error is influenced. There is a countermeasure method to again correct a pitch error correction value using a correction value corresponding to weights of the respective workpieces, but it is necessary to input previously measured weights of the workpieces to the controller.
When workpieces having the same weight are continuously machined, a weight of a workpiece which is machined first is measured, and this measured weight can be used and thus, there is no problem. However, when workpieces having different weights are continuously machined, since it is necessary to measure the weight in each case, the weight-measuring operation of the workpiece requires labor. When measured weight data is erroneously input to the controller, the correction amount cannot precisely be calculated.
When a workpiece which is to be electric discharge machined is fixed to a table using a jig, in order to precisely correct a pitch error, it is necessary to take a weight of the jig into account. Like the workpiece, there is a problem that a machine body of a casting or a guide is distorted under the influence of the weight of the jig, and a pitch error is influenced.
There is a countermeasure method to again correct a pitch error correction value using a correction value corresponding to weights of the respective workpieces, but it is necessary to input the previously measured weight of the jig into the controller. When jigs having the same weight are continuously used, a weight of a jig which is first used is measured, and the value can be used and thus, there is no problem. However, when jigs having different weights are used, since it is necessary to measure the weight in each case, the weight-measuring operation of the jigs requires labor. When measured weight data of the jigs is erroneously input to the controller of the electric discharge machine, the correction amount cannot precisely be calculated. When materials of workpieces and jigs are different from each other, an operation for detaching the workpieces and the jigs from the machine to measure the weights individually, such an operation requires labor.
A technique disclosed in JP 2012-192512 A is characterized in that a weight of machining liquid obtained by mixing liquid and oil is measured using a measuring tank, and liquid of a reduced amount is replenished. The reduced amount of machining liquid is computed based on density of computed machining liquid, density of liquid and density of oil based on volume of machining liquid and weight of the machining liquid. There is a problem that to measure the weight, a tank for measuring is separately required.